Refactor tool execution pipeline

tools/datetime/src/main.rs

@@ -0,0 +1,14 @@
+//! datetime — 本地时间
+
+use chrono::Local;
+
+fn main() {
+    let _ = std::io::stdin().read_line(&mut String::new());
+    let now = Local::now();
+    let out = serde_json::json!({
+        "type": "result",
+        "content": format!("当前时间: {}\n星期: {}\n时区: {}",
+            now.format("%Y-%m-%d %H:%M:%S"), now.format("%A"), now.offset())
+    });
+    println!("{out}");
+}